Silph Co, for me, is the most memorable part of Pokemon Red/Blue. Sure before this you went through two caves, a Cruise Ship, Pokemon Tower and the underground basement of a casino filled with Team Rocket, but, nothing up to this point, or even after compared to Silph Co. Silph Co was a huge twoer located in Saffron City that has been taken hostage by Team Rocket. A lot of the buildings including the gym is blocked off by Team Rocket, making it a mandatory to complete the game. Silph Co is a huge tower that consists of 11 floors each one filled with maze like corridors, items to pick up, teleportation tiles that take you to different areas in the building and team rocket grunts trying to take you down. A monumental part of the game needs a great theme and the one used delivers.
The Silph Co theme is like a tension rollercoaster; as from the very beggining the theme ascends like a pressure chamber while at the same time you ascend the tower taking out Team Rocket members one by one; reaching the top to face Giovanni. This theme has been stuck in my head for so long probably because this part of the game takes so long; making the theme play over and over and over again until it is installed in your brain, but I don't mind because it ended up being my favorite in the game. See what a little repetition does, it make a memorable theme.
Note: Once again this song was not uploaded by me but done by this guy.